Overview The X-ray Crystallography Core facility provides excellent crystallization, data collection, and crystallographic computing facilities. It also provides outstanding human resources in the form of talented crystallographers and a strong training environment. Location of the Core facilities adjacent to the Hill, Sundquist, and Kay labs on the third floor of the EEJMRB provides a convenient and accessible environment that maximizes productive formal and informal interactions. A postdoctoral fellow and a student within this Core are dedicated to Center projects (VPS4 and ALIX). The two managers and technician (50:50 with Bacterial Expression Core) provide expertise and support for additional projects. The core can also support use by other Center personnel and projects as appropriate. For example, Steve Alam (Manager Eukaryotic Protein Expression Core) recently played the lead role on determination of the EAP45(ESCRTII) GLUE-ubiquitin crystal structure with assistance from Frank Whitby17; Anna Scott determined the structure of human VPS4B with assistance from Whitby19; Schubert played the lead crystallographic role on the TSG101-ubiquitin complex20, and Andy VanDemark, a postdoc in the Hill lab, recently determined crystal structures of a potent HIV-1 entry inhibitor complex with the gp41 N-peptide (submitted) and a sterically restricted N-peptide antigen (in preparation) in collaborations with the Kay lab. The strength of the Core is enhanced by interactions with major national facilities and structural genomics consortia. Extensive use of remote data collection services (e.g, at NSLS and SSRL) typically enables synchrotron data collection within about a week of identifying a suitable crystal. We routinely utilize the Hauptman-Woodward Institute crystallization facility of the Northeastern Structural Genomics Consortium. This approach provided initial conditions that led to the preliminary crystals of dodecameric Vps4p after vapor diffusion trials failed at our home lab. We recently initiated a novel collaboration with the Joint Centers for Structural Genomics that will allow the full power of high-throughput methodology to be applied to the focused scientific questions being addressed by our program. This arrangement will also allow us to accommodate a potentially high demand for assistance with crystal structure determinations by the larger community of HIV biologists, such as through the R21 and other mechanisms.